This PR

• sorts packages by importance (platform packages first, then PHP dependencies) and alphabetically

Follows #3549.

💡 Not sure if anyone but me uses that feature, but it would be a lot nicer if packages were sorted by importance (platform packages first), then followed by PHP dependencies, both sorted alphabetically.

See https://getcomposer.org/doc/02-libraries.md#platform-packages.

• php represents the PHP version of the user, allowing you to apply constraints, e.g. >=5.4.0. To require a 64bit version of php, you can require the php-64bit package.
• hhvm represents the version of the HHVM runtime (aka HipHop Virtual Machine) and allows you to apply a constraint, e.g., >=2.3.3.
• ext-<name> allows you to require PHP extensions (includes core extensions). Versioning can be quite inconsistent here, so it's often a good idea to just set the constraint to *. An example of an extension package name is ext-gd.
• lib-<name> allows constraints to be made on versions of libraries used by PHP. The following are available: curl, iconv, icu, libxml, openssl, pcre, uuid, xsl.